This application is a divisional application of patent application Ser. No. 09/541,135, filed Mar. 31, 2000, titled “Method of Forming Scribe Line Planarization Layer,” issued as U.S. Pat. No. 6,383,894.
1. Field of the Invention
The invention relates to wafer processing and more particularly to introducing colorants on a wafer.
2. Description of Related Art
Integrated circuit chips use colorants for a variety of applications. One common application is the use of a chip as an image sensor to capture a color image in a digital imaging system. In one example, the image sensor is a semiconductor chip made up of a number of photosensitive circuits, each photosensitive circuit capable of absorbing light. In color applications, each photosensitive circuit generally absorbs light through a color filter that represents a particular wavelength of light in the visible spectrum corresponding to the image sensed. The color filter generally contains a colorant, such as a pigment or dye.
A CMOS- or CCD-based image sensor is typically formed as a chip or die of a wafer of a number of chips and dies with each chip or die separated from one another by a scribe line or scribe line area. Once formed, the wafer is singulated into individual chips or dies using conventional wafer dividing tools. The chips or dies are singulated, for example, by sawing the wafer through the scribe line area.
In color applications, color filter array (CFA) material is introduced over a photosensing region or area of the chip or die. CFA material is typically a photoimageable material. The material is typically spin-coated on a wafer, baked, and exposed to ultraviolet light through a mask to crosslink or polymerize the CFA material where desired. The remainder of the CFA material is then removed.
A typical photoimageable CFA material is a two-phase material of an acrylic resin and an organometallic pigment. For spin-coating operations, the CFA material is usually combined into a solution with a casting solvent/dispersing agent to keep the pigment in solution. The solution is generally thixotropic in the sense that it has a variable viscosity. The spinning process tends to change this viscosity. There is also generally a step height between a chip or die and the scribe line area, such as for example, a step height on the order of five microns (μm). During a spinning operation of CFA material onto a wafer, there is a tendency to form inconsistencies, such as striations or different color patterns (e.g., different color saturation), brought about by physical forces associated with spinning CFA material in the presence of a step height. These striations or different color patterns translate into a systemic noise in the system.
What is needed is a technique for reducing striations of colorants in wafer processing, particularly involving spin-on processes of material containing a colorant.